1. Field of the Invention
The present invention relates to a bump stopper which is employed in a suspension system of a vehicle, for elastically limiting the amount of operation of the suspension system.
2. Related Art Statement
There is known a bump stopper which is formed of an elastic material and which is employed in, e.g., a suspension system of an automotive vehicle, for limiting elastically a stroke amount of a wheel which is elastically supported such that the wheel is movable relative to the vehicle's body, or assisting the suspension system in supporting elastically the wheel. The bump stopper is provided solely between two suspension arms, or between a suspension arm and the body, or is externally fitted on a piston rod of a shock absorber. The bump stopper is required, for the purpose of simultaneously meeting high ride quality and high stability and controllability, to have a non-linear spring characteristic wherein the stopper is soft while the amount of operation of the suspension system is small but it changes to be hard, once the operation amount exceeds a reference amount, so as to limit reliably the operation amount around the reference amount.
To this end, there has been proposed a bump stopper which includes a generally cylindrical spring member having a low spring constant and a rigid restraint ring externally fitted on, and fixed to, an outer circumferential surface of an axially intermediate portion of the spring member. The restraint ring may be formed of resin. In this bump stopper, the restraint ring prevents the spring member from elastically swelling radially outwardly. In addition, when the amount of compression of the spring member exceeds a reference mount, the restraint ring butts against another rigid member and accordingly the movement of the ring is limited by that rigid member. Consequently, the spring characteristic of the bump stopper changes to be much harder to limit effectively the amount of elastic deformation of the spring member and accordingly the amount of operation of the suspension system.
However, in the above-identified bump stopper, the elastic deformation of the spring member is locally or non-uniformly limited by the restraint ring. Therefore, when the spring member is elastically deformed and the amount of elastic deformation increases, stresses are likely to be concentrated at the position where the restraint ring is provided. Thus, the durability of the spring member is lowered.
In the case where the restraint ring frequently butts against the rigid member upon inputting of a large load to the suspension system, or in the case where the ring butts with a great force or energy against the rigid member, the durability of the ring or the rigid member is also lowered. If the restraint ring breaks, the bump stopper cannot effectively limit the amount of elastic deformation of the spring member, so that the stability and controllability of the vehicle may be significantly lowered.